Polyolefin stabilizer comprised of a boric acid ester, a phenolic inhibitor and a sulfur-containing costabilizer



United States Patent POLYOLEFIN STABILIZER COMPRISED OF A BORIC ACID ESTER, A PHENOLIC INHIBITOR AND A SULFUR-CONTAINING COSTABILIZER Delos E. Bown, Eugene E. Poirot, and Raymond A.

Speed, Baytown, Tex., assignors, by mesne assignments,

to Esso Research and Engineering Company, Elizabeth,

N.J., a corporation of Delaware No Drawing. Filed July 30, 1962, Ser. No. 213,159

9 Claims. (Cl. 26045.85)

The present invention is directed to an improved composition including a polyolefin. More particularly, the invention is concerned with a polyoleiin composition which has improved oxidative stability, thermal stability, and color. In its more specific aspects, the invention is directed to a polypropylene composition which has been stabilized against degradation caused by oxidation and exposure to elevated temperatures and against color instability.

The present invention may be briefly described as a polyolefin composition such as polypropylene which contains a major amount of a solid polymer of an alpha olefin having 2 to 8 carbon atoms in the molecule and a minor amount of :an ester of boric acid. It is contemplated that the composition of the present invention may contain a phenolic inhibitor and a costabilizer.

In the practice of the present invention, the boric acid ester may be employed in an amount within the range from about 0.01 to about 1.0 percent by weight of the solid polymer. An amount within the range from about 0.1 to about 0.5 percent by weight may be preferred.

The boric acid ester is represented by the esters of boric acid having the formula:

/OR BOR where R is selected from the group consisting of alkyl radicals having 1 to carbon atoms, mono-aryl radicals, alkyl mono-aryl radicals having 1 to 10 alkyl carbon atoms, and the naphthenyl radicals. Specific compounds of this nature may be illustrated by: triethyl borate, tri-m or p-cresyl borate, tri-n-propyl borate, tri-isopropyl bo-r ate, 2,6-di-t butylphenyl di-n-butyl borate, 2,6-di-t-butyl4- methylphenyl di-n-butyl borate, tribenzyl borate, tIi-ocnaphthyl borate, tri-n-butyl borate, triphenyl borate, phenyl di-n-propyl borate, and diphenyl m-butyl borate.

The phenolic type inhibitor may be illustrated by compounds such as dipinene diphenol and other stabilizers such as exemplified by a ,a -bis(3t-butyl-5-methyl-2-hydroxyphenyl)mesitol, 2,6-di-tbutyl-4-methylphenol, 4,4- thiobis- 3-met-hyl-6-1t-butylphenol 4,4'-( 1,1-butylidene) bis-(3-methyl-6-t-butylphenol) 2,6 bis(a-phenethy-l)-4- methylphenol, 2,6-bis(.1,l-dimethyl-n-octyl) 4 methylphenol, 2,2 methylenebis (4 methyl-6-t-butylipheno1), and 4,4'-methylenebis-(2,6-di-t-butylphenol).

The amount of the phenolic inhibitor may be an amount within the range from about 0.01 to about 1.0 percent by Weight of the composition and an amount within the range from about 0.01 to about 0.5 percent by weight may be preferred.

it is also desirable in the practice of the present invention to employ a sulfur-containing costabilizer such as illustrated by the d-ialkyl sulfides having 12 to 30 carbon atoms in the molecule of which illustrative members are diotadecyl sulfide, didocosyl sulfide, diheptadecyl sulfide, ditricosyl sulfide, dipentadecyl sulfide, ditet-racosyl sulfide, dinonadecyl sulfide, dipentacosyl sulfide, dieicosyl sulfide, dihexacosyl sulfide, diheneicosyl sulfide, and diheptacosyl sulfide. Other sulfur-containing compounds may be used, of which dilauryl thiodipropionate is preferred. Other sulfur-containing compounds such as distearyl thiodipropionate, 19,ZS-dithiohentetetracontane, 19,24 dithiotetracontane, bis (octadecylmercaipto)-p-xyl ylene and -bis(tetradecylmercapto)-p-xylylene may be employed.

The dipinene diphenol employed in the composition is a resinous material with the pinene and phenol being present in a ratio of about 1:1. The dipinene diphenol has a molecular Weight in the range from about 450 to about 550 and may be represented by the formula:

The dipinene diphenol is produced by reacting 1 mol of pinene and 1 mol of phenol in the presence of boron trifiuoride etherate as a catalyst at a temperature from about F. to about 122 F. to form the resinous dipinene diphenol product. In preparing the dipinene diphenol, a mixture of alpha and beta pinene in a benzene solution of phenol is reacted. The product is washed with hot Water to remove catalyst and unreacted material. Thereafter, the washed product is dried, filtered, and then distilled to remove benzene and any light fraction. The material remaining is the dipinene diphenol. The dipinene diphenol has a ring and ball melting point in the range from about C. to about C. and is completely soluble in methanol.

The polyolefin polymers employed in the practice of the present invention are polymers of olefins having 2 to 8 carbon atoms in the molecule and may suitably be exemplified by polyethylene, poly-propylene, ethylenepropylene copolymers, ethylene-butene-l copolymers, ethylene-pentene-l copolymers and the like having molecular Weights in the range from about 10,000 to about 1,000,000. These polymers are produced by polymerization of the corresponding olefins employing the Ziegler type polymerization catalyst which is obtained by at least partially reducing in solution in a diluent a halide of an amphoteric metal selected from Groups IV-B, V-B, VIB, and VIII of the Periodic System of Elements, such as the Henry D. Hubbard Periodic Chart of the Elements, 1947, ed. revised by W. F. Meegers; W. M. Welch Mfg. Co., Chicago, Ill. Examples of suitable halides from which the catalyst is prepared are the halides of titanium, zirconium, hafnium, thorium, uranium, vanadium,

3 columbium, tantalum, chromium, molybdenum, tungsten and mixtures thereof. Exemplary of suitable compounds include titanium tetrachloride, titanium tetrabromide, zirconium tetrachloride and the like.

In preparing catalyst suitable for use in forming the polymer treated in accordance with the present invention, the amphoteric metal halide is reduced in solution in a nonreactive, nonpolar organic diluent in any suitable manner such as by means of chemical reaction with a suitable chemical compound having reduction properties, by irradiation, and the like. This is done to reduce at least a portion, and preferably more than about 30 percent, of the amphoteric metal halide to a lower valence state. The product of the reaction step comprising the diluent and the at least partially reduced amphoteric metal halide is employed as a medium in which olefin polymerization is effected.

The diluent to be employed should be a nonreactive, nonpolar organic medium in which the amphoteric metal halide starting material is soluble to an extent at least sufficient to provide a 0.1 weight percent solution of an amphoteric metal halide starting material. Thus, for example, in preparing the polymerization medium, a 0.1 to 10 weight percent solution of amphoteric metal halide in the diluent may be employed.

Among the diluents that may be employed are saturated aliphatic hydrocarbons preferably containing from about 5 to carbon atoms per molecule. Specific examples of such diluents include pentane, hexane, heptane, octane, decane, nonane, and isomers and mixtures thereof or other saturated petroleum hydrocarbons. A- particularly desirable diluent is n-heptane. It will be understood that other hydrocarbon diluents may be used such as aromatic hydrocarbon diluents as exemplified by benzene, xylene and the like; halogenated hydrocarbons such as monochlorobenzene, dichlorobenzene and the like; gas oil distillate fractions obtained from the catalytic cracking or vis-breaking of gas oil feed stock; Diesel oil; and the other similar hydrocarbon fractions. It will be understood that, if desired, mixtures of two or more compatible miscible diluents may be employed. The diluents should be substantially completely free from oxygen, water and similar compounds of strong polarity which are reactive with the products obtained by reduction of the amphoteric metal halide.

The nonpolar organic liquid in which the slurry is formed may suitably be identical with the diluent in which the catalyst is formed for polymerization of the olefinic hydrocarbons.

The polymerization reaction is suitably conducted at temperatures in the range from about -60 F. to about 400 F., preferably at about room temperature. Higher temperatures may be employed but are generally undesirable in that catalyst decomposition may be encountered. Subatmospheric pressures and pressures up to about 250 atmospheres may be employed in forming the polymer which is produced in accordance with the present invention. It is generally preferable to employ in the polymerization technique a comparatively low pressure, and specifically it is desirable to employ atmospheric pressure. Reaction times may vary within the range from about 10 minutes to about 24 hours.

As a result of subjecting the olefins of the type illustrated before to treatment with the catalyst of the nature described, olefin polymers are formed having the molecular weights recited which are essentially insoluble in the nonpolar organic liquid and form a slurry of polymerized olefins in the nonpolar organic liquid. These 4 polymers are quenched to reactivate any catalyst by adding methanol and the like thereto, and additional quantities of methanol may be added to the slurry to allow separation of the polymer particles. The polymer particles after separation from the slurry, are treated by adding the several compounds thereto. Thus, the phenolic inhibitor, the sulfur-containing costabilizer and the boric acid ester may be added severally or together to the polymer particles. Since the polymer particles as recovered from the slurry are in a finely divided state, they have a high surface area and rapidly adsorb oxygen. It is, therefore, desirable in accordance with the present invention to add the boric acid ester, the phenolic inhibitor and. the sulfur-containing costabilizer thereto to prevent color degradation and to impart oxidative and thermal stability to the composition.

The boric acid ester may be suitably added to the polymer by blending the boric acid ester with the polymer pellets and then the blend is extruded to provide dispersion. Aromatic hydrocarbon solutions of the boric acid ester may be added to the dry polymer powder and the mixture worked or extruded to form a homogeneous mixture or composition. Suitable aromatic hydrocarbons as solvents are benzene, toluene, xylenes, and the like, as well as other solvents in which the boric acid ester will dissolve.

In adding the phenolic inhibitor and the sulfur-containing costabilizer to the solid polymer, thsee materials may suitably be employed and incorporated in the solid polymer by forming a solution of the particular additives in a suitable solvent such as, for example, an aromatic hydrocarbon, a low boiling ether such as diethyl ether, an aliphatic alcohol such as methanol, or by dissolving the phenolic inhibitor and the sulfur-containing costabilizer in a solvent such as xylene, hexane and the like. The phenolic inhibitor and the sulfur-containing costabilizer may be sprayed over pellets or particles of the polymer and the resulting mixture may then be extruded through a suitable extrusion device to cause formation of a homogeneous mixture. While it is preferred to add the phenolic inhibitor and the sulfur-containing costabilizer as a solution, these materials may suitably be added as such to the polymer particles and the resulting mixture subjected to milling and/or extrusion as desired to cause intimate admixture of the two materials with the polymer composition to form a homogeneous mixture. While extrusion and milling have been described as modes of incorporating not only the boric acid ester but also the phenolic inhibitor and sulfur-containing costabilizer into the polymer, other means may suitably be employed so long as the boric acid ester, particularly, and the phenolic inhibitor and the sulfur-containing costabilizer are thoroughly distributed throughout and admixed with the polymer.

The composition of the present invention is quite important and useful in formation of products such as molded and extruded devices and articles; or the polyolefin composition after suitable addition of the dialkyl sulfide and the phenolic costabilizer may be formed into films for use in wrapping foodstuffs and other articles; or the polymer composition may be extruded as a filament to be used in weaving and forming of cloth, fibers and otherv similar materials.

In order to illustrate the practice of the present invention, a number of compositions were made up in which a boric acid ester was added to a 'high molecular weight polyolefin, polypropylene, to determine the effect thereof on oxidative stability, thermal stability, and color. Compositions were made up without the boric acid ester butwith other additives for comparative purposes. The amount of the several additives incorporated into the polypropylene and the tests following table:

thereof are shown in the cosity of the sample after it has been heat treated in the TABLE I E fleet of triisopropyl borate on polyproplene powder stability Sample Metal Com- P.p.m. Color 01 Injection Oxidative No. Stabilizer System Wt. Percent pound Added as .Color MI. Sr Molded Pads Stability,

Metal Days S181 DLTDP, Argus D, Inol .25, .05, 1+ 4.9. 4.8 23. S217- DLTDP, Argus D, Iouol..- .25, .05, .15 FeCl fi 11 -0.. 5 3 4. 2 6. 7 1

S280-- DLTDP, Argus D, 101101 .25, .05, .15, .1 FeCl .6 11 0...- 5 1+ 4. 0 2.0 24

Isopropyl Polyborate.

8-313..- DLTDP, Argus D 1 5. 2 2. 5 28 S317 DLTDP, Argus D FeC]a.6 1120.". 5 3+ 5. 9 3.9 8 2 S-319 DLTDP, Argus D, FeClafi 120..-. 5 1+ 3.9 2.1

propyl Borate.

S325 DLTDP, Polybisphenol .5, .05 1+ 4. 5 1.3 White e 12 Phosphite, Zn2Et. Hex. 8-327.-. DLTDP, Polybisphenol 5, .5, .0, 5.1 1 3. 5 0.9 Very White e 18 Phosphite, Zn2Et. Hex., Triisopropyl Borate.

S326 DLTDP, Polybisphenol .5, .5, .05, .6 1 3. 0 2.3 Otf White (Opaque)... e 24 Phosphite, Zn2Et. Hex., 1 Oxanalide. S328 DLTDP, Polybisphenol .5, .5, .05, .6, .1 1 3.3 2.2 White (Opaque) B Phosphite, Z112Et. Hex., Oxanalide, Triisopropyl Borate.

8-360--- DLTDP, Dipinene Di- 1, .02, .03 2 6.0 3.1 011 White 15 phenol, Zinc Stearate. 8-301"... DLTDP, Dipinene Di- 1, D2, .03, 1 2 4. 2 2. 6. White phenol, Zinc Stearate, Triisopropyl Borate.

8-434..- DLTDP, Dipinene Di- 1, .02, .03 1 5.9 2.7 White 12 phenol, Zinc Stearate. S-435 DLTDP, Dipinene Di- 1, 02, .03, .05 1 3.4 2. 7 do phenol, Zinc Stearate, Triisopropyl Borate.

S-385 DLTDP, Dipinene Di- 1, .02, .03 2+ 6. 4 2. 0 011 White 16 phenol, Zinc Stearate. S-461- DLTDP, Dipinene Di- 1, 02, .03, .02 1+ 4. 8 1. 7 White 58 phenol, Zinc Stearate, 'Iriisopropyl Borate.

S-364 DLTDP, Dipinene Di- 2, .03, .03 3+ 3.3 2. 7 Yellow 40 phenol, Zinc Stearate. S-363 DLTDP, Dipinene Di- 2, .03, .03, .1 1+ 2.7 2.6 Light Yellow 80 phenol, Zinc Stearate, Triisopropyl Borate.

S-424 DLTDP, Dipinene Diphe- 2, .03, .03 1+ 3.3 5.0 011 White 36 1101, Zinc Stearate. 8-448-.- DLTDP, Dipinene Diphe- 2, .03, .03, .1 1 2. 9 3. 5 White 83 I101, Zinc Stearate, Triisopropyl Borate. S462 DLTDP, Argus G .25, .05 1 4.2 5. 0 White 24 S463 DLTDP, Argus G, Triiso- .25, .05, .05 1- 4.1 2. 4 do 25 propyl Borate.

S445 DLTDP, Dipinene Diphel, .02, .03 1 6.2 2.9 White 6 n01, Zinc Stearate. S-479 DLTDP, Dipinene Diphe- 1, 02, .03, .05 1 3.3 1 2.9 -do (27) nol, Zine Stearate, Tri-npropyl Borate.

S-474 DLTDP, Argus G .25, .05 1+ 4.9 i 3.6 White 30 8-475-.. DLTDP, Argus G, Tri-n- 25, .05, .1 l 5. 2 2.9 .do b (36) propyl Borate. 1

8 With copper screen. b Still on test, no evidence of breakdown.

It Will be seen from the results of these tests shown in Table I that an improvement in color is obtained when a boric acid ester is added to polpypropylene polymers. Also, the thermal stability is improved as will be evidenced bythe melt index (MI) and the S data shown in the table. The S value is a direct measure of the thermal stability of a polymer sample, and compares the original 7 truded and pelletized.

absence of air at 550 F. for 30 minutes. Likewise, an

improvement in oxidative stability is obtained.

Whereas the data of Table I illustrate the effectiveness of boric acid esters when they are incorporated into polypropylene powder, the data of Table II illustrate that the boric acid esters are also effective when they are incorporated into polypropylene which has already been ex- TABLE II Finished polypropylene pellets-Efiect of triisopropyl borate Oxidative Sample Original Color Stability N0. Stabilizer System Wt. percent Color Improvement (315 F., a 7 Oxygen) Hours DLTDP, ArgusD .30, .l 2+-.-.- 6 P-2 DLTDP, Argus-D, Triisopropyl 84 Borate.

...... DLTDP, Dipinene Diphenol 244 P-8 DLTDP, Dipiuene Diphenol, Tri- 520 isopropyl Borate.

. DLTDP, Dipinene Diphenol 504 P-9 DLTDP, Dipinene Diphenol, Tri- 624 isopropyl Borate.

DL'IDP, Argus-D. 10 P12 DLtIDI, Argus-D, Triisopropyl Bor- 33 DLTDP, Argus-D. .24, .05 1 6 P-14. DIETDP, Argus-D, Triisopropyl Bor- .24, .05, None 10 DLIDP, ArgusD .31, .15 1+ 6 P DLTDP, Argus-D, Triisopropyl Bor- .31, .15, Slight 11 ate,

It will be seen from the data in Table II that the presence of triisopropyl borate improved the oxidative stability of the several compositions.

In Tables I and II, abbreviations have been used to designate various additives added to the polypropylene. These additives are identified as follows:

1) Argus D: a mixture of zinc 2-ethyl hexanoate, 4,4'-thiobis(3 methyl 6-t-butyl phenol) and a mixture of triphenyl phosphite and triisooctyl phosphite.

(2) Ionol: 2,6-di-t-butyl-4-methylphenol.

(3) DLTDP: dilauryl thiodiopropionate.

(4) Argus G: a mixture of zinc Z-ethyl hexanoate, 4,4-isobutylidene bis(3 methyl-6-t-butyl phenol) and a mixture of triphenyl phosphite and triisooctyl phosphite.

Polyolefins, such as polypropylene, sometimes exhibit poor color and poor stability which may be caused by the presence of metal contaminants such as catalyst residues, including titanium and aluminum, iron, nickel, copper and the like. The use of polyolefins such as polypropylene as electrical insulators results in contamination of the polypropylene with copper which causes degradation of the polypropylene. In accordance with the present invention, this discoloration and degradation is suppressed or completely eliminated by adding boric acid ester to the polyolefin. The boric acid esters prevent discoloration and degradation even when good color polymer is heated to approximately 550 F. during molding operations. The discoloration and degradation may occur even when the polymer has been inhibited with a good oxidative stabilizer system; for example, Ionol and dilauryl thiodipropionate, or Ionol, dilauryl thiodipropionate and Argus D or Argus G (commercially available products of the Argus Chemical Corporation).

The nature and objects of the present invention having been completely described and illustrated and the best mode thereof set forth, what we wish to claim as new and useful and secure by Letters Patent is:

1. A composition having improved oxidative stability, thermal stability and color which comprises a solid polymer of an alpha olefin having 2 to 8 carbon atoms in the molecule containing a copper contaminant and an amount within the range from about 0.01% to about 1.0% by Weight of a boric acid ester having the formula:

where R is selected from the group consisting of alkyl radicals having 1 to 10 carbon atoms, mono-aryl radicals, alkyl mono-aryl radicals having 1 to 10 alkyl carbon atoms, and naphthenyl radicals, and also containing effective amounts within the range from about 0.01% to about 1.0% of a phenolic inhibitor selected from the group consisting of dipinene diphenol, a ,o -bis(3-t-butyl- 5 -methyl-2-hydroxyphenyl) mestiol, 2,6 di t butyl 4 methylphenol, 4,4-thiobis- 3-methyl-6-t-butylphenol) 4, 4-(1,1-butylidene)bis-(3-rnethyl 6 t-butylphenol), 2,6- bis( a-phenethyl -4-methylphenol, 2,6-bis(1,1-dimethyl-noctyl -4-methyl-phenol, 2,2'-rnethylenebis-(4-methyl-6-tbutylphenol) and a co-stabilizer selected from the group consisting of dialkyl sulfides having 12 to 30 carbon atoms in the molecule, dilauryl thiodipropionate, distearyl thiodipropionate, 19-25-dithiohentetetracontane, 19,24-dithiotetracontane, bis(octadecylmercapto)-p-xylylene and bis(tetradecylmercapto)-p-Xylylene.

2. A composition in accordance with claim 1 in which the solid polymer is polyethylene.

3. A composition in accordance with claim 1 in which the solid polymer is polypropylene.

4. A composition in accordance with claim 1 in which the costabilizer is a dialkyl sulfide.

5. A composition in accordance with claim 1 in which the solid polymer is present in an amount within the range from about 99.0% to about 99.9% by weight.

6. A composition in accordance with claim 1 in which the boric acid ester is triisopropyl borate.

7. An article comprising a copper surface in contact with a solid polymer of an alpha mono-olefin having 2 to 8 carbon atoms in the molecule containing an effective amount of a boric acid ester having the formula:

BOR

where R is selected from the group consisting of alkyl radicals having 1 to 10 carbon atoms, mono-aryl radicals, alkyl mono-aryl radicals having 1 to 10 alkyl carbon atoms, and naphthenyl radicals sufiicient to overcome the deleterious effect of said metal surface on said polymer, and also containing effective amounts within the range from about 0.01 to about 1.0% of a phenolic inhibitor selected from the group consisting of dipinene diphenol, a ,a -bis(3-t-butyl-5-methyl-2-hydroxyphenyl) mesitol, 2,

4,4-methylenebis-(2,6-di-t-butylphenol),

9 6-di-t-butyl-4-methylphenol, 4,4 thiobis (3-methyl-6-tbutylphenol), 4,4 (1,1 buty1idene)bis (3 methyl-6+ hutylphenol), 2,6-bis(a-phenethyl)-4-methylpheno1, 2,6- bis(1,1-dimethyl-n-octyl) 4 methylphenol, 2,2'-methylenebis-(4-methyl-6-t-butylphenol) 4,4'-metl1ylenebis-(2, 6-di-t-butylphenol), and a costabilizer selected from the group consisting of dialkyl sulfides having 12 to 30 carbon atoms in the molecule, dilauryl thiodipropionate, distearyl thiodipropionate, 19,25-dithiohentetetracontane, 19,24-dithiotetracontane, bis(octadecylmercapto) p Xylylene and bis(tetradecylmercapto)-p-xylylene.

8. An article in accordance with claim 7 in which the mono-olefin is propylene.

9. An article in accordance with claim 7 in which the mono-olefin is ethylene.

10 References Cited by the Examiner UNITED STATES PATENTS FOREIGN PATENTS 6/ 1961 Great Britain.

LEON I. BERCOVITZ, Primary Examiner.

15 DONALD E. CZAJA, Examiner. 

1. A COMPOSITION HAVING IMPROVED OXIDATIVE STABILITY, THERMAL STABILITY AND COLOR WHICH COMPRISES A SOLID POLYMER OF AN ALPHA OLEFIN HAVING 2 TO 8 CARBON ATOMS IN THE MOLECULE CONTAINING A COPPER CONTAMINANT AND AN AMOUNT WITHIN THE RANGE FROM ABOUT 0.01% TO ABOUT 1.0% BY WEIGHT OF A BORIC ACID ESTER HAVING THE FORMULA: 